1. Field of the Invention
This invention relates to an improved design for a centrifugal pumping stage of a multi-stage, axially stacked, centrifugal pump of the type employed in oil wells.
2. Description of the Prior Art
As oil wells are drilled and completed to increased depths for production, the pumping requirements, particularly the pressure head to be developed by the pumping apparatus, have increased in more than direct proportion to the well depth. A conventional form of pump employed for pumping fluid from deep oil wells is the multi-stage centrifugal pump wherein a plurality of pumping stages are axially stacked, one upon the other, and driven by a common shaft. Since the diameter of the pumping apparatus is positively limited by the internal diameter of the well casing, and the motor speed is limited to less than 3600 RPM, if 60 cycle current is employed, it has heretofore been only possible to increase the effective pressure head developed by the electric motor driven multi-stage pump by adding additional pumping stages.
In addition to the diametrical constraint imposed by the interior diameter of the well casing, there must also be recognized the fact that the electric power supply to the pump motor must be carried down through the casing and, even though this may represent a cable having a diameter of one-half inch or less, this further reduces the size of the exterior dimensions of the housing for the pumping stages that can be inserted in the casing. The wall thickness of the cylindrical housing for the multi-stage pumping apparatus obviously is determined by the very substantial tensile forces exerted on such housing when the entire assembly of one hundred or more stages is incorporated within the housing and lowered into position in the well. These restraints thus produce an unchangeable maximum diameter within the multi-stage pump housing in which the pumping elements must operate.
In many oil fields, pumping stages on the order of two hundred to three hundred units are often required to develop the required pressure head. A modest increase in pressure developed by each stage of such multi-stage pumps could therefore effect a significant reduction in the number of stages required. For example, a ten percent increase in pumping head per stage in a two hundred stage pump would result in a reduction of a number of pumping stages required by twenty. If such pressure increase could be accomplished with no decrease in efficiency, the substantial cost savings would be self-evident.